This invention relates to a magnetic recording apparatus and a magnetic recording method, and more particularly, to a magnetic recording apparatus and a recording method which realize a super-high-density magnetic recording that exceed the thermal-agitation limit of a recording medium.
With improvement in the processing speed of a computer in recent years, magnetic memory storage, such as HDD (Hard Disk Drive) which performs recording and reproduction function of information or data, is needed to have a higher recording density and a higher operating speed. However, it is said that there is a physical limit in a recording density.
By using the conventional method, it is thought to be difficult to continue meeting the demand of high speed and high recording density in the future.
In the case of HDD apparatus, the magnetic recording medium with which information is recorded has a magnetic layer containing the aggregate of fine magnetic particles.
In order to perform a high-density recording, it is necessary to make the magnetic domains smaller, which are recorded on the magnetic layer. In order to be able to distinguish small recording magnetic domains, it is required for the boundaries of the magnetic domains to be smooth enough.
For that purpose, it is necessary to make minute magnetic particles which are contained in the magnetic layer.
If magnetization reversal carries out a chain even to an adjoining magnetic particle, “disorder” of the boundary of a magnetic domain is caused. Therefore, the magnetic particles need to be magnetically divided each other by a non-magnetic body so that an exchange-coupling interaction may not work between the magnetic particles. Besides, from a viewpoint of the magnetic interaction between a recording head and a medium, it is also necessary to make the thickness of the magnetic layer thin enough in order to perform a high-density recording.
Thus, it is necessary to make still smaller volume of the magnetization reversal unit in a magnetic layer from the above request. If the above-mentioned demand is completely filled, the volume of the magnetization reversal unit in a magnetic layer will ultimately become almost equal to a volume of the magnetic particle. However, if a magnetization reversal unit is made minute, the magnetic anisotropy energy (a product Ku×Va where Ku is a density of magnetic anisotropy energy and Va is a volume of magnetization reversal unit) of the unit will become smaller than thermal-agitation energy. Therefore, it becomes impossible for a magnetic reversal unit to hold the magnetic domains.
This is the thermal-agitation phenomenon which serves as the main factor of the physical limit (called a “thermal agitation limit”) of a recording density.
In order to prevent undesired reversal of the magnetization by the thermal-agitation, the density of magnetic anisotropy energy Ku may preferably be enlarged. However, at the time of recording, i.e. when performing high-speed magnetization reversal operation in the case of the above-mentioned HDD medium, a coercive force Hcw is proportional to Ku mostly. Therefore, by using the magnetic field which the conventional recording head may generate, recording will become impossible, if Ku is enlarged.
In order to prevent reversal of the magnetization by the thermal-agitation, enlarging volume Va of a magnetization reversal unit is also considered. However, if Va is enlarged by increasing the size of the magnetic particle in a medium, high-density recording cannot be attained. Besides, if Va is enlarged by thickening film thickness of the recording layer, a magnetic field from the head will not fully reach the lower part of the recording layer. Therefore, magnetization reversal will not take place and high-density recording cannot be attained too.
Furthermore, since it is difficult to produce recording and a reproducing head in minute size, it is becoming difficult to attain high-density recording.
According to the situation explained above, there are many problems in the case of the conventional recording and reproducing method using the recording magnetic field from the magnetic recording head, and detecting a stray magnetic field from a recorded pattern by a reproducing head. Therefore, in order overly to attain high-density recording, it is necessary to newly develop recording and reproducing method using an electrical current etc.